Conventional turbomachines (also referred to as turbines), such as steam turbines (or, steam turbomachines), generally include static nozzle assemblies that direct the flow of working fluid (e.g., steam) into rotating buckets that are connected to a rotor. In steam turbines the nozzle (or, airfoil) construction is typically called a “diaphragm” or “nozzle assembly” stage. Nozzle assemblies are assembled in two halves around the rotor, creating a horizontal joint. At the horizontal joint are packings which prevent steam leakage across the rotor. Traditional packings use a key at the horizontal joint to prevent the packings in the upper half from dropping out during assembly/disassembly, and to inhibit rotation of the packings in their slots (or, dovetail slots) should the rotor contact the packings during operation. Gravitational forces keep the packing segments in the lower half in place.
In variable clearance positive pressure packings (VCPPP), two separate key designs are used for the upper and lower half. These packings use pressure to activate the location of the seals during operation, from an open radial position to a closed radial position. Because these packings move radially as a function of steam load, a key is used for the lower half packings to keep the left and right packing segments from dropping into the middle packing segment and preventing the packing segments from closing properly. A key for the VCPPP design serves two purposes: (1) to retain the packing segments; and (2) to allow for motion of the packing in the radial direction.
However, conventional key configurations for retaining packing segments (e.g., VCPPP packing segments) in the lower half of a turbine require significant real estate, add high sensitivity to calculations due to the friction between the key and ring, and have mechanical disadvantages associated with bending stresses, local wear, and distortion of parts. For more contemporary steam path designs, the spacing between the bucket and nozzles is shrinking, and the radial inner ring height is also getting smaller. These factors make it difficult to retain turbine packings in a manner that occupies little real estate while maintaining limited friction and proper location of the packing.